Voltammetric capacities

From the experimentally determined values Aq(E) the voltammetric capacity C i E) was calculated by differentiating Aq numerically with respect to ... 

From these voltammetric capacity data an equilibrium voltammogram ... 

Figure 7 Voltammetric capacities Cvoit( of pT and pOPh films, (a) PT films type pTl in 85% H3PO4. (b) PT films type pT2 in IM H3PO4. (c) POPh films type CSP in IM H2SO4.

The reason for this loss in capacity with increasing scan can be clearly seen in the voltammograms in Fig. 30A and 30A. The peak separation, discussed in detail above, becomes larger as the scan rate is increased. The result of this enhanced distortion of the voltammetric wave is the inability to utilize the capacity of the electrode over the useful potential window of the electrode (3.0 to 1.5 V). As would be expected (see above), this distortion is less for the microtubular electrode, and this should result in higher capacities for this electrode. 

The study of hydrogen and deuterium electrosorption in palladium limited volume electrodes (LVE) was carried out by the same group in both acidic and basic solutions [124,130,134]. It was found that the hydrogen capacity, H (D)/Pd, measured electrochemically, depends significantly on sweep rate in cyclic voltammetric experiments and also on the thickness of the LVE. Two different mechanisms of hydrogen desorption, that is, the electrochemical oxidation and the nonelectrochemical recombination step, which take place in parallel within the Pd—LVE, have been postulated. 

For the pseudo-capacity of adsorbed intermediates and for double-layer charging, cyclic voltammetric currents increase linearly with the sweep rate. For diffusion-controlled currents, the variation of the current increases with the square root of the sweep rate. 

FeTi with the addition of 6% Nb, or 10% Mn or Ni, has been studied with respect to hydrogen absorption [553]. The presence of Nb enhances hydrogen absorption but the catalytic activity appears to be lower than that of NiTi. Impedance and voltammetric measurements have been used. The presence of 10% Mn in FeTi increases its hydrogen storage capacity slightly, whereas 20% Ni decreases it by ca. 20-30%. The enthalpies of hydride formation have been determined [537]. 

Apart from acidification, UV irradiation is the only preliminary preparative step in voltammetric determinations it may be required to degrade organic substances binding trace metals in the form of inert complex species. The analysis of samples from natural waters may be significantly affected by the binding capacity of such dissolved organic substances. 

If we register the second harmonic current vs. d.c. potential, this will have the same form as the second derivative of the voltammetric curve, as Fig. 11.11 shows. One of the advantages of the use of the second harmonic is that, since the double layer capacity is essentially linear, it contributes much less to the second harmonic than to the fundamental frequency and the calculation of accurate kinetic parameters is much facilitated. 

To conclude this section, it should be emphasized that the steady state vol-tammograms described above are quite different from the first scan of the cyclic voltammetry of these systems. During the first polarization of these electrodes to low potentials, pronounced reduction processes of solution components are observed. As a result of these processes, a stable precipitate forms on the electrodes as insoluble films, and hence the above steady state voltammetric behavior reflects electrochemistry which is surface film controlled. The outer, solution side of these films is probably porous, leading to the high interfacial capacity which is reflected by the relatively high non-Faradaic currents which characterize these voltammograms. The next section describes in detail the initial voltammetric behavior of these systems and the surface film formation on the electrodes. 

Voltammetric procedures can be used for trace measurements of diltiazem. Diltiazem exhibits both reductive and oxidative voltammetic responses. Adsorptive stripping voltammetry can be used due to the reductive capacity of diltiazem. The adsorptive stripping is accomplished with a static mercury drop electrode in conjunction with a stripping analyzer. A detection... 

Consider the application of a charge step sufficiently large that the potential changes from eq to value, E t = 0), corresponding to the diffusion plateau of the voltammetric wave. We assume that the double-layer capacity, Q, is independent of potential in this region. The faradaic current that flows under these conditions at a planar electrode is given by (5.2.11). Introduction of this expression into (8.7.4) yields... 

Gulaboski R, Mirceski V, Mitrev S. Development of a rapid and simple voltammetric method to determine total antioxidative capacity of edible oils. Food Chem. 138(1) (2013) 16-121. 

Cyclic voltammetric data, even when using a three-electrode potentiostat form of instrumentation, can be affected by the presence of uncompensated resistance in the solution phase between the reference and the working electrode and of the working electrode itself, and by the capacity of the working electrode. A simple electrochemical cell may be described by an equivalent circuit, in which electronic... 

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